1. Field of the Invention
The present invention relates to a network address conversion system, and in particular to a network address conversion system for enabling access to a node having a private IP address, a method therefor, and a recording medium for recording the method. The present application is based on Korean Patent Application No. 2000-49934, which is incorporated herein by reference.
2. Description of the Related Art
Recently, a number of information communication devices such as computers, faxes, modems, and telephones can be used in a network in a single office.
The networks provided in small office home offices (SOHO) and homes are mostly private networks, in which a gateway has a global IP address, while the other information communication devices do not have global IP addresses.
Accordingly, the respective information communication devices (that is, network nodes) of the private network have private IP addresses which can only be used for internal purpose.
The private IP address is provided by a network administrator or automatically provided through a communication protocol, such as Dynamic Host Configuration Protocol (DHCP).
In addition, the network nodes have port numbers. At this time, the port number implies a communication protocol in the network node.
However, it is expected that the network nodes of the private network having the private IP addresses will have to provide services to external network nodes on the Internet.
For this, the external Internet must be able to access the network nodes of the private network.
Currently, the gateway (network entrypoint) of the private network converts the private IP address of the private network into a public IP address, and thus the network node using the private IP address of the private network can access a node of the Internet to use services.
As an exemplary address conversion method, there is a network address port translation (NAPT). In the NAPT, when the network node of the private network intends to access the external node, a node corresponding to a network entrypoint allocates an external port value, thereby externally transmitting a packet.
A conventional network address conversion system on the Internet will now be explained with reference to the accompanying drawings.
FIG. 1 is a structure diagram illustrating a general network system on the Internet.
As illustrated in FIG. 1, a private network 20 is a SOHO or home network which connects a plurality of information communication devices.
The private network 20 includes one gateway node 21 and a plurality of network nodes 20a, 20b, . . . , 20n. The gateway node 21 is a modem, router, gateway or switch which has a public IP address. The private network 20 is connected to the Internet 10 through the gateway node 21.
In addition, the plurality of network nodes 20a, 20b, . . . , 20n are information communication devices connected through the network, such as desktop computers, notebook computers, printers, and faxes.
The network nodes 20a, 20b, . . . , 20n have private IP addresses internally used in the private network 20.
Here, the public IP address of the private network 20 is SIP, and the private IP addresses and port numbers of the nodes 20a–20n are respectively (LIP1, LPN1), (LIP2, LPN2), . . . , and (LIPn, LPNn).
A few private networks such as an office network 30 and a home network 40 are connected to the Internet.
A network node 12 has a public IP address and provides a service on the Internet. The public IP address and port number of the network node 12 are DIP and PD.
The private network nodes of the office network 30 and the home network 40 can access the network node 12 in order to receive the Internet service from the network node 12.
A conventional network address conversion method when the node 20a accesses the network node 12 will now be described.
FIG. 2 is a flowchart showing sequential steps of the conventional network address conversion method, and FIG. 3 shows a signal flow in a state where the network node of the private network accesses an external network node of the Internet.
In FIG. 3, D denotes an address and port number of a destination, and S denotes an address and port number of a source.
First, the node 20a of the private network 20 transmits a packet to the network node 12 to use services (step S202). The packet includes the address and port information (LIP1, LPN1) of the source and the address and port information (DIP, PD) of the destination.
The gateway node 21 having the public IP address receives the packet (step S204), allocates a new port number Px to the private IP address and port number (LIP1, LPN1) of the source node 20a (step S206), and records a mapping relation in a conversion table (step S208).
Thereafter, the gateway node 21 converts the source information of the received packet, by using the public IP address SIP and the newly-allocated port number Px (step S210).(LIP1, LPN1)→(SIP, Px)
The gateway node 21 transmits the converted packet through the Internet. According to the source information, the packet is transmitted to the network node 12 (step S212).
The network node 12 performs an operation according to the contents of the packet, generates a response packet, and transmits the response packet through the Internet (step S214).
Here, the source information and the destination information are exchanged, and thus the destination information becomes (SIP, Px).
According to the destination information, the response packet is transmitted to the gateway node 21 of the private network 20 which has the public IP address of SIP.
The gateway node 21 receiving the response packet converts the port number Px of the destination information into a value stored in the conversion table (step S216).(Px)→(LIP1, LPN1)
Therefore, the response packet is transmitted to the node 20a having the address and port number of (LIP1, LPN1), namely the node transmitting the packet requesting use of the services (step S218).
On the other hand, the gateway node 21 deletes the value stored in the conversion table (step S220).
As described above, in the conventional network address conversion system on the Internet, the node of the private network can transmit data to the external node of the Internet.
However, the private IP address cannot be used on the Internet. As a result, the Internet node cannot demand a service from the node of the private network.